Product evolution in the Np(IV) fluorophosphate system

• Published in: Journal of solid state chemistry Vol. 180; no. 1; pp. 70 - 74
• Main Authors: Bray, Travis H., Sullens, Tyler A., Shvareva, Tatiana Y., Sykora, Richard E., Haire, Richard G., Albrecht-Schmitt, Thomas E.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01-01-2007; Elsevier
• Subjects: CESIUM CARBONATES; Condensed matter: structure, mechanical and thermal properties; CRYSTALLIZATION; CRYSTALLOGRAPHY; Exact sciences and technology; GALLIUM OXIDES; HEATING; HYDROFLUORIC ACID; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; MONOCLINIC LATTICES; MONOCRYSTALS; Neptunium crystal structure; Neptunium fluoride; NEPTUNIUM FLUORIDES; Neptunium fluorophosphaste; Neptunium phosphate; ORTHORHOMBIC LATTICES; PHOSPHATES; PHOSPHORIC ACID; Physics; SPACE GROUPS; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; TEMPERATURE RANGE 0400-1000 K; Neptunium phosphate; Neptunium crystal structure; Neptunium fluorophosphaste; Neptunium fluoride; Phosphates; Space groups; Crystallization; Ternary alloys; Fluorides; Monoclinic lattices; Neptunium; Heat treatments; Gallium oxides; Monocrystals; Actinides; Hydrothermal synthesis; Impurities; Three dimensional structure; Hafnium; Orthorhombic lattices; IV characteristic; Crystal structure
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2006.09.019

The reaction of
237NpO
2 with Cs
2CO
3, Ga
2O
3, H
3PO
4, and HF under mild hydrothermal conditions leads to the formation of NpFPO
4 after 4 days at 180
°C. Heating at 180
°C for an additional 6 days leads to the crystallization of Cs
2Np
2F
7PO
4 and NpF
4. The Ga
2O
3 forms a GaPO
4 matrix in which crystals of NpFPO
4, Cs
2Np
2F
7PO
4, and NpF
4 grow. Single crystal X-ray data reveal that the structure of NpFPO
4 consists of Np(IV) centers bound by both fluoride and phosphate to yield [NpF
2O
6] distorted dodecahedra. These are linked by corner-sharing with fluoride and both corner- and edge-sharing with phosphate to yield a dense, three-dimensional network. The structure of Cs
2Np
2F
7PO
4 is complex and contains both distorted dodecahedral [NpO
2F
6] and tricapped trigonal prismatic [NpO
2F
7] environments around Np(IV) that are linked with each other through corner- and edge-sharing, and with the phosphate groups to create a three-dimensional structure. There are small channels extending down the
a-axis in Cs
2Np
2F
7PO
4. Crystallographic data: NpFPO
4, orthorhombic, space group
Pnma,
a=8.598(2),
b=6.964(1),
c=6.337(1)
Å,
Z=4,
V=379.44(13)
Å
3, R(F)=3.53% for 40 parameters and 465 reflections with
I>2σ(
I) (
T=193
K); Cs
2Np
2F
7PO
4, monoclinic, space group
P2
1/
c,
a=8.8727(4),
b=16.2778(7),
c=7.8009(4) Å,
β=112.656(1),
Z=4,
V=1039.73(8) Å
3, R(F)=2.27% for 146 parameters and 2465 reflections with
I>2σ(
I) (
T=193
K).
Two Np(IV) fluorophosphates, NpFPO
4 and Cs
2Np
2F
7PO
4, have been prepared as single crystals under hydrothermal conditions. NpFPO
4 crystallizes first, then reacts to yield Cs
2Np
2F
7PO
4 and finally yields NpF
4. Single crystal X-ray structures of NpFPO
4 and Cs
2Np
2F
7PO
4 show three-dimensional frameworks containing Np(IV) in both eight- and nine-coordinate environments.